Simplest Editor TextAdornment

Add a border around each line.

namespace Microsoft.VisualStudio.Text.Editor
{
  using Microsoft.VisualStudio.Text.Formatting;
  using Microsoft.VisualStudio.Utilities;
  using System.ComponentModel.Composition;
  using System.Windows;
  using System.Windows.Controls;
  using System.Windows.Media;

  [Export(typeof(IWpfTextViewCreationListener))]
  [ContentType("text")]
  [TextViewRole(PredefinedTextViewRoles.Document)]
  internal sealed class TextAdornment1Factory : IWpfTextViewCreationListener
  {
    [Export(typeof(AdornmentLayerDefinition))]
    [Name("TextAdornment1")]
    [Order(After = PredefinedAdornmentLayers.Selection, Before = PredefinedAdornmentLayers.Text)]
    public AdornmentLayerDefinition editorAdornmentLayer = null;

    public void TextViewCreated(IWpfTextView textView)
    {
      new TextAdornment1(textView);
    }
  }

  public class TextAdornment1
  {
    IAdornmentLayer layer;
    IWpfTextView view;

    public TextAdornment1(IWpfTextView view)
    {
      this.view = view;
      layer = view.GetAdornmentLayer("TextAdornment1");

      this.view.LayoutChanged += OnLayoutChanged;
    }

    private void OnLayoutChanged(object sender, TextViewLayoutChangedEventArgs e)
    {
      foreach (ITextViewLine line in e.NewOrReformattedLines)
      {
        this.CreateVisuals(line);
      }
    }

    private void CreateVisuals(ITextViewLine line)
    {
      IWpfTextViewLineCollection textViewLines = view.TextViewLines;

      Geometry g = textViewLines.GetMarkerGeometry(line.Extent);
      if (g != null)
      {
        var border = new Border
        {
          Width = g.Bounds.Width,
          Height = g.Bounds.Height,
          BorderBrush = Brushes.Violet,
          BorderThickness = new Thickness(0.8),
        };

        Canvas.SetLeft(border, g.Bounds.Left);
        Canvas.SetTop(border, g.Bounds.Top);

        layer.AddAdornment(AdornmentPositioningBehavior.TextRelative, line.Extent, null, border, null);
      }
    }
  }
}

Exercises

1. Add a border around each line, bypassing initial spaces.

   namespace Microsoft.VisualStudio.Text.Editor
   {
     using Microsoft.VisualStudio.Text.Formatting;
     using Microsoft.VisualStudio.Utilities;
     using System.ComponentModel.Composition;
     using System.Text.RegularExpressions;
     using System.Windows;
     using System.Windows.Controls;
     using System.Windows.Media;
   
     [Export(typeof(IWpfTextViewCreationListener))]
     [ContentType("text")]
     [TextViewRole(PredefinedTextViewRoles.Document)]
     internal sealed class TextAdornment1Factory : IWpfTextViewCreationListener
     {
       [Export(typeof(AdornmentLayerDefinition))]
       [Name("TextAdornment1")]
       [Order(After = PredefinedAdornmentLayers.Selection, Before = PredefinedAdornmentLayers.Text)]
       public AdornmentLayerDefinition editorAdornmentLayer = null;
   
       public void TextViewCreated(IWpfTextView textView)
       {
         new TextAdornment1(textView);
       }
     }
   
     public class TextAdornment1
     {
       IAdornmentLayer layer;
       IWpfTextView view;
   
       public TextAdornment1(IWpfTextView view)
       {
         this.view = view;
         layer = view.GetAdornmentLayer("TextAdornment1");
   
         this.view.LayoutChanged += OnLayoutChanged;
       }
   
       private void OnLayoutChanged(object sender, TextViewLayoutChangedEventArgs e)
       {
         foreach (ITextViewLine line in e.NewOrReformattedLines)
         {
           this.CreateVisuals(line);
         }
       }
   
       private void CreateVisuals(ITextViewLine line)
       {
         IWpfTextViewLineCollection textViewLines = view.TextViewLines;
         int start = line.Start;
   
         var m = new Regex(@"\S").Match(line.Extent.GetText());
         if (m.Success) start += m.Index;
         
         var span = new SnapshotSpan(line.Snapshot, Span.FromBounds(start, line.End));
   
         Geometry g = textViewLines.GetMarkerGeometry(span);
         if (g != null)
         {
           var border = new Border
           {
             Width = g.Bounds.Width,
             Height = g.Bounds.Height,
             BorderBrush = Brushes.Violet,
             BorderThickness = new Thickness(0.8),
           };
   
           Canvas.SetLeft(border, g.Bounds.Left);
           Canvas.SetTop(border, g.Bounds.Top);
   
           layer.AddAdornment(AdornmentPositioningBehavior.TextRelative, span, null, border, null);
         }
       }
     }
   }
       

2. Highlight spaces.

   namespace Microsoft.VisualStudio.Text.Editor
   {
     using Microsoft.VisualStudio.Text.Formatting;
     using Microsoft.VisualStudio.Utilities;
     using System.ComponentModel.Composition;
     using System.Text.RegularExpressions;
     using System.Windows;
     using System.Windows.Controls;
     using System.Windows.Media;
   
     [Export(typeof(IWpfTextViewCreationListener))]
     [ContentType("text")]
     [TextViewRole(PredefinedTextViewRoles.Document)]
     internal sealed class TextAdornment1Factory : IWpfTextViewCreationListener
     {
       [Export(typeof(AdornmentLayerDefinition))]
       [Name("TextAdornment1")]
       [Order(After = PredefinedAdornmentLayers.Selection, Before = PredefinedAdornmentLayers.Text)]
       public AdornmentLayerDefinition editorAdornmentLayer = null;
   
       public void TextViewCreated(IWpfTextView textView)
       {
         new TextAdornment1(textView);
       }
     }
   
     public class TextAdornment1
     {
       IAdornmentLayer layer;
       IWpfTextView view;
   
       public TextAdornment1(IWpfTextView view)
       {
         this.view = view;
         layer = view.GetAdornmentLayer("TextAdornment1");
   
         this.view.LayoutChanged += OnLayoutChanged;
       }
   
       private void OnLayoutChanged(object sender, TextViewLayoutChangedEventArgs e)
       {
         foreach (ITextViewLine line in e.NewOrReformattedLines)
         {
           this.CreateVisuals(line);
         }
       }
   
       private void CreateVisuals(ITextViewLine line)
       {
         IWpfTextViewLineCollection textViewLines = view.TextViewLines;
         int start = line.Start;
         int end = line.End;
   
         for (int i = start; i < end; i++)
         {
           if (line.Snapshot[i] == ' ')
           {
             var span = new SnapshotSpan(line.Snapshot, Span.FromBounds(i, i + 1));
   
             Geometry g = textViewLines.GetMarkerGeometry(span);
             if (g != null)
             {
               var border = new Border
               {
                 Width = g.Bounds.Width,
                 Height = g.Bounds.Height / 8,
                 BorderBrush = Brushes.Black,
                 BorderThickness = new Thickness(0.8, 0, 0.8, 0.8),
               };
   
               Canvas.SetLeft(border, g.Bounds.Left);
               Canvas.SetTop(border, g.Bounds.Bottom - g.Bounds.Height / 8);
   
               layer.AddAdornment(AdornmentPositioningBehavior.TextRelative, span, null, border, null);
             }
           }
         }
       }
     }
   }
       

3. TBD

4. TBD